Polyurethane polymers are generally produced by the reaction of a polyisocyanate, particularly diisocyanates, with hydroxyl-rich compounds containing at least two hydroxyl groups per molecule, such as glycols, polyester and polyether polyols or amine-rich compounds such as aromatic and aliphatic diamines and polyamines. The extensive industrial use of polyurethane polymer and the production thereof is accompanied by a considerable accumulation of waste or scrap polyurethane polymer. Such scrap polymer may be disposed of by techniques including incineration or landfill. However such disposal techniques, besides not giving full consideration to the environment, essentially lead to the permanent loss of costly materials as used in the preparation of polyurethane polymer. It is therefore of interest to consider the recovery and eventual reuse of such materials.
Procedures of recovering the chemicals in scrap polyurethane polymer are known in the art. U.S. Pat. No. 2,937,151 discloses dissolving flexible polyurethane foams in liquid polyalkylene glycol ethers, polyester or polyesteramides. U.S. Pat. No. 3,632,530 discloses decomposition of a polyurethane by heating in the presence of an aliphatic diol such as ethylene glycol or dipropylene glycol. However, in practice, methods for recovering scrap polyurethane based on degradation of the foams in the presence only of alcohol groups are excessively time consuming, even in the presence of catalysts, such as taught in U.S. Pat. No. 3,300,417. An increased rate of dissolution of the scrap urethane foam by the use of primary amines in place of alcohols is taught in U.S. Pat. No. 3,117,940. U.S. Pat. No. 3,708,440 discloses the dissolution of isocyanurate foam in a mixture of diethylene glycol and diethanolamine. U.S. Pat. No. 3,404,103 discloses decomposing polyurethane in an aliphatic amine, e.g. monoethanolamine, and the presence of an alkali metal oxide or alkali metal hydroxide, such as sodium hydroxide, to obtain an amine derivative and a polyether; separating the polyether from the amine derivative and reemploying the polyether for production of urethane polymer.
All of the procedures noted above yield a mixture of polyols, aromatic and aliphatic ureas, and aromatic and aliphatic amines, and occasionally some soluble urethane fragments. Further such mixtures, as obtained according to the above noted procedures, frequently undergo a phase separation into a low density and viscosity polyol component and a higher viscosity and density amine component. Such two phase mixtures besides being more difficult to handle must always be well mixed before they can be used in any subsequent application or else there is little or no control of reproducibility and consistency of results. The susceptibility of the recovered material to phase separation becomes greater as the amount of scrap polymer to be treated per unit volume solvent increases. Additionally, the presence of frequently odorous amine is generally undesirable when using recovered material to prepare a fresh polyurethane polymer as it may enhance the reactivity of the system to such an extent that only poor quality polymer articles may result. Accordingly it is generally required that such amine content be removed from the mixture. Suitable techniques for the removal of the amine component include, for example, distillation procedures such as disclosed in U.S. Pat. Nos. 3,404,103; 4,316,992; 4,317,939 and 4,399,236. However, separation of polyol and amine components is undesirable due to additional energy and labor costs.
As an alternative to removing the amine component from the recovered mixture, the complete mixture may be further treated with an alkylene oxide. Such treatment as disclosed in, for example, U.S. Pat. Nos. 3,738,946 and 4,110,266 converts the amine functionality to less reactive hydroxyl functionality thus facilitating the reuse of such material in the preparation of fresh polyurethane polymer.
Despite the seemingly extensive disclosure of recovery/recycling technology for waste or scrap polyurethane polymer there still remains a need to provide a process which provides a more useful recovered material and is economically advantageous to operate. Particularly it is desirable to provide a process which allows, in a relatively shorter period of time, the recycling of large volumes of scrap material without encountering phase separation. It is further desirable that such process provide for a product that may be appropriately treated to give an end product which is substantially free of any hydrogen-bearing nitrogen atoms.